2 Answers
2

The phrase "the story of [some person]" implies that I'm talking about the most important or most significant story about that person. For example, if I say "the story of Bill Gates," I mean the story of how Bill Gates co-founded Microsoft and became the richest person in the world. On the other hand, if I say "a story of Bill Gates," I mean some story which involves Bill Gates, but not necessarily the most significant story about Bill Gates.

So, if you write

The novel tells the story of a salesman.

then you're probably telling the story of the salesman's entire life, or the story of how he became a successful salesman, or something like that.

On the other hand, if you write

The novel tells a story of a salesman.

then you're telling some story about the salesman, but not necessarily a particularly important story.

You can also say "a story about a salesman" instead of "a story of a salesman"; I think "about" sounds a little more natural than "of" in this context. However, you can't say "the story about a salesman" instead of "the story of a salesman," because the phrase used to refer to a person's life story is "the story of," not "the story about."

This, ladies and gentlemen, is a good answer.
– Ben KovitzOct 4 '19 at 4:12

@BenKovitz Second that. This answer makes it clear that both the definite and indefinite articles are fine in the sentence at issue and gives an excellent explanation. This answer should have been accepted.
– Eddie Kal♦Feb 11 at 20:15

The definite article (the) is used for the nouns you are sure of, definite of.

By putting the novel itself means that the context is clear and they are referring to the specific novel. Furthermore, when it is clear which novel they are talking about, and when that novel becomes specific, the story is also already defined. That is why, you put the.

In short, in the given sentence, both of them are defined - the novel and the story of someone.